This invention broadly relates to a method for manufacturing an oxide thin-film for use in a bolometer and to a non-cooling type infrared ray sensor using the oxide film.
A bolometer utilizes temperature variation of electrical resistance of a metal film or a semiconductor film which is thermally insulated from a substrate material. A temperature coefficient of electrical resistance (TCR) and electrical resistance value are exemplified as characteristics required for materials for the bolometer.
In general, as the electrical resistance value of the material for the bolometer becomes higher, Johnson noise also becomes higher. This phenomenon is not preferable.
On the other hand, when the electrical resistance becomes low, a difference between wiring resistance other than the bolometer and an electrical resistance value of the material for the bolometer becomes small. This phenomenon is not desirable also.
In consideration of the above, it is desirable that the electrical resistance value of the material for the bolometer falls within the range between 5 and 100 Kxcexa9 at the room temperature.
In other words, if a resistive element thin-film for the bolometer has a thickness within the range between 50 and 1,000 nm, electrical resistivity required for the material for the bolometer desirably falls within the range between about 0.025 and 10 xcexa9cm.
In addition, temperature resolution of an infrared ray sensor (NETD) is inversely proportional to a TCR absolute value of the material for the bolometer. Accordingly, the infrared sensor having lower NETD can be obtained by using the material for the bolometer with a higher TCR absolute value.
Generally, an alloy thin-film such as a nickel iron alloy has TCR of about 0.5%/K, and as a result, it is not preferable for the bolometer material of the infrared rays sensor with high sensitivity.
In contrast, a vanadium oxide thin-film has a relatively high TCR of about 2%/K as disclosed in Japanese Unexamined Patent Publication (JP-A) No. Hei. 11-271145. Consequently, it is generally used for the material of the bolometer.
Alternatively, a part of vanadium V is attempted to be replaced by the other element such as manganese Mn disclosed in Japanese Unexamined Patent Publication (JP-A) No. 2000-143243. In consequence, it has been reported that the TCR absolute value can be increased up to about 4%/K.
However, the material having higher TCR for the bolometer must be developed in order to achieve further higher sensitivity or multiple pixels of the infrared ray sensor.
To achieve such a purpose, suggestion has been made about use of a provskite type Mn oxide represented by La1xe2x88x92x Srx MnO3, La1xe2x88x92x Cax MnO3, Pr1xe2x88x92x Srx MnO3 as the material for the bolometer.
This technique utilizes such phenomenon that the perovskite type Mn oxide has high TCR within a semiconductor region, thus obtaining a value of about 3%/K as the TCR absolute value.
However, this value is not particularly high compared to such a case that a part of vanadium oxide base is replaced by Mn. To this end, the infrared rays sensor utilizing the characteristic of the semiconductor region of the perovskite type Mn oxide does not has a specific advantage in comparison with the infrared ray sensor using the conventional vanadium oxide based material.
In contrast, another attempt has been made about use of the other characteristics of the above perovskite type Mn oxide for the infrared ray sensor, as disclosed Japanese Unexamined Patent Publication (JP-A) No. 2000-95522.
The above perovskite type Mn oxide has a unique characteristic indicative of phase transition between an insulator and a metal. In such phase transition, the provskite type Mn oxide transfers from an insulating state of high temperature into a metal state of low temperature in accordance with variation of magnetic property.
Under this circumstance, the temperature, at which the transition between the insulator and the metal occurs, can be set near the room temperature by adjusting Sr composition x in the above La1xe2x88x92x Srx MnO3.
In this case, the electrical resistance is largely varied in the transition between the insulator and the metal, thus obtaining higher TCR. By employing such characteristic, it is expected that the infrared ray sensor with higher sensitivity can be realized compared to the conventional sensor. In practical, it has been reported that the material has excessively high TCR of 5% K or more, particularly exceeding 10%/k.
Thus, the infrared ray sensor can have high sensitivity or multiple pixels by utilizing the perovskite type Mn oxide as the material for bolometer. However, a sol-gel method is used during producing the perovskite type Mn oxide thin-film in the aforementioned JP-A No. 2000-95522.
As described in the above Patent Publication, for example, each coating agent for octane based MOD method (organic metal deposition) of La, Sr, Mn is mixed with a desired ratio, is applied on an oxide substrate, is dried, and then is annealed for crystallization at a high temperature.
In this event, it is necessary to anneal at high temperature of approximately 1000xc2x0 C. in order to realize an excellent transition between the insulator and metal in the perovskite type Mn oxide thin-film.
As the other methods, use is made of a deposition method such as a laser ablation method or a sputtering method. For example, as described in applied physics letters (Appl. Phys. Lett.) 74 volume. 290 page, 1999, high deposition temperature of 700xc2x0 C. or more is required so as to obtain the excellent transition between the insulator and the metal even when these deposition methods will be used.
As discussed above, high TCR exceeding 5%/K can be obtained by utilizing the transition between the insulator and the metal inherent to the perovskite type oxide. Consequently, it is expected that the non-cooling type infrared ray sensor with higher sensitivity than the conventional case can be realized by using the perovskite type Mn oxide as the material for the bolometer.
Generally, a receiving portion of the non-cooling type infrared ray sensor is formed on a Si substrate. Further, a signal read-out circuit is arranged in the Si substrate under the receiving portion. On the other hand, the resistive element for the bolometer is formed on a bridge structure body placed on the Si substrate via a thermal insulating gap.
Specifically, the resistive element for the bolometer is formed on the Si substrate having the signal read-out circuit. To this end, the material for the bolometer must have consistency with a Si production process in addition to the high TCR.
From viewpoint of the consistency with the Si production process, it is required that deposition temperature is low at 400xcx9c500xc2x0 C. or less and that a physical etching method such as ion-milling can not be utilized during forming the pattern of the resistive element for the bolometer. This is because the physical etching gives damage for the signal read-out circuit of Si formed on an under layer.
Considering such a problem with respect to the production process, the perovskite type Mn oxide thin-film has important disadvantages as the material for the bolometer.
First, as described above, the high deposition temperature is necessary in order to increase TCR with this material, namely, to obtain the excellent transition between the insulator and the metal. More specifically, the temperature of about 1000xc2x0 C. is necessary in the case of the sol-gel method while the temperature of 700xc2x0 C. or higher is required in the sputtering method.
As long as the high deposition temperature is required, it is difficult to apply the attractive material having high TCR to the Si production process.
Practically, the thin-film is merely formed on SrTiO3 (100) resistant to high deposition temperature, namely, on an oxide single crystal substrate instead of the Si substrate according to an embodiment disclosed in the above-mentioned JP-A No. 2000-95522.
Second, a reactive ion etching method is not applicable to form the pattern of the resistive element for the bolometer by processing the perovskite type Mn oxide film. In consequence, the physical etching method such as the ion-milling must be used, thus making it difficult to apply the perovskite type Mn oxide thin-film to the material for the bolometer.
It is therefore an object of this invention to provide a non-cooling infrared ray sensor of a bolometer type with high sensitivity.
It is another object of this invention to provide an oxide thin-film for a bolometer with high TCR and a method for manufacturing an infrared ray sensor using the thin-film.
According to a first aspect of this invention, an oxide for use in a bolometer with an oxide thin-film formed is manufactured on an insulating substrate.
Under this circumstance, metal organic compound is dissolved in solvent to form solution during manufacturing the oxide thin-film.
Then, the solution is applied on the insulating substrate, and the applied solution is dried.
Next, a bond between carbon and oxygen is cut and decomposed by irradiating a laser ray with wavelength of 400 nm or less. Successively, a generated oxide is crystallized.
Here, the oxide thin-film is composed of a perovskite type Mn oxide represented by A1xe2x88x92x Bx Mn O3 (0 less than x less than 1).
Intensity of radiation energy irradiated by measuring electrical resistance of the oxide thin-film is measured by the bolometer. Herein, A is triatomic rare metal, and B is diatomic alkali rare metal.
According to a second aspect of this invention, the earth metal of the perovskite type Mn oxide is at least one selected from the group consisting of La, Nd, and Pr or composite thereof.
According to a third aspect of this invention, the alkali earth metal of the perovskite type Mn oxide is at least one selected from the group consisting of Ca, Sr, and Ba or composite thereof.
According to a fourth aspect of this invention, the laser ray is an excimer laser ray selected from the group consisting of ArF, KrF, XeCl, XeF, and F2.
According to a fifth aspect of this invention, the laser lay is irradiated with multiple stages.
According to a sixth aspect of this invention, the laser ray is irradiated not to completely decompose the metal organic compound at an initial state and to crystallize the perovskite type Mn oxide at a subsequent stage.
According to a seventh aspect of this invention, the irradiation of the laser ray is carried out by heating the insulating substrate applied with the metal organic compound under a temperature 500xc2x0 C. or less.
According to a eighth aspect of this invention, the insulating substrate is a perovskite type oxide single crystal thin-film selected from the group consisting of SrTiO3, LaAlO3, and NdGaO3.
According to a ninth aspect of this invention, the metal organic compound comprises metal organic acid salt.
According to a tenth aspect of this invention, metal of the metal organic acid salt is at least one selected from the group consisting of La, Nd, Pr, Ca, Sr, Ba, and Mn.
According to a eleventh aspect of this invention, organic acid of the metal organic acid salt is at least one selected from the group consisting of naphthenic acid, 2-ethyl hexanoic acid, caprylic acid, stearic acid, lauric acid, acetic acid, propionic acid, oxalic acid, citric acid, lactic acid, benzonic, salicylic acid, and ethylenediaminetetraacetic acid.
According to a twelfth aspect of this invention, the metal organic compound comprises metal acetylacetonato complex.
According to a thirteenth aspect of this invention, the metal acetylacetonato complex is at least one selected from the group consisting of La, Nd, Pr, Ca, Sr, Ba, and Mn.
According to a fourteenth aspect of this invention, solvent for dissolving the metal acetylacetonato complex is at least one selected from the group consisting of butyl acetate, toluene, acetylacetone, and methanol.
According to a fifteenth aspect of this invention, the perovskite type Mn oxide thin-film formed by the manufacturing method of the first aspect is used as a resistive element for the bolometer in an infrared ray sensor.
According to a sixteenth aspect of this invention, the sensor has a micro-bridge structure.
According to a seventeenth aspect of this invention, the infrared ray sensor is manufactured as follows.
Initially, the resistive element for the bolometer is set on the insulating substrate applied with the metal organic compound. Herein, the resistive element has a pattern portion.
Then, the laser ray with the wavelength of 400 nm or less is irradiated only for the pattern portion through a mask for transmitting the laser ray to form the perovskite type Mn oxide.
Finally, a non-irradiation portion is removed by dissolving using a solvent to directly form a pattern of the resistive element for the bolometer.
According to an eighteenth aspect of this invention, the laser light lay is irradiated with multiple stages such that the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a nineteenth aspect of this invention, the laser ray is irradiated not to completely decompose the metal organic compound at an initial state and to crystallize the perovskite type Mn oxide at a subsequent stage. Thereby, the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a twentieth aspect of this invention, the irradiation of the laser ray is carried out by heating the insulating substrate applied with the metal organic compound under a temperature 500xc2x0 C. or less such that the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a twenty-first aspect of this invention, the insulating substrate is a perovskite type oxide single crystal thin-film selected from the group consisting of SrTiO3, LaAlO3, and NdGaO3.
According to a twenty-second aspect of this invention, a strong laser ray occurring ablation is initially irradiated on the insulating substrate applied with the metal organic compound through a mask pattern for masking the pattern portion of the resistive element for the bolometer during forming the resistive element for the bolometer.
Then, the mask is removed.
Next, the laser ray with the wavelength of 400 nm or less is irradiated to form directly the perovskite type Mn oxide as the pattern of the resistive element for the bolometer.
According to a twenty-third aspect of this invention, the second laser ray irradiation is carried out by irradiating the laser ray with the wavelength of 400 nm or less with multiple stages. Thereby, the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a twenty-fourth aspect of this invention, the laser ray is irradiated not to completely decompose the metal organic compound at an initial state and to crystallize the perovskite type Mn oxide at a subsequent stage. Thereby, the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a twenty-fifth aspect of this invention, the irradiation of the laser ray is carried out by heating the insulating substrate applied with the metal organic compound under a temperature 400xc2x0 C. or less such that the pattern of the resistive element for the bolometer is directly formed on the insulating substrate.
According to a twenty-sixth aspect of this invention, the insulating substrate is a perovskite type oxide single crystal thin-film selected from the group consisting of SrTiO3, LaAlO3, and NdGaO3.
More specifically, according to this invention, the perovskite type oxide thin-film with the temperature coefficient of the electrical resistance can be deposited at low temperature by the optical reaction using the laser light ray in the method for manufacturing the oxide thin-film for the bolometer and the infrared ray sensor.